package com.lanou.moving.utils;

import android.support.v4.view.ViewPager.PageTransformer;
import android.view.View;

/**
 * Created by dllo on 15/11/4.
 */
public class ZoomOutPageTransformer implements PageTransformer{
    private static float MIN_SCALE = 0.85f;

    private static float MIN_ALPHA = 0.5f;

    @Override
    public void transformPage(View view, float position) {
        int pageWidth = view.getWidth();
        int pageHeight = view.getHeight();

        if (position < -1) { // [-Infinity,-1)
            // This page is way off-screen to the left.
            //小于-1时候 page在屏幕外 设置为全透明
            view.setAlpha(0);
        } else if (position <= 1) { // [-1,1]
            // Modify the default slide transition to
            // shrink the page as well

            //设置缩放系数 最小系数和...中取较大值
            float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
            //设置竖直边距
            float vertMargin = pageHeight * (1 - scaleFactor) / 2;
            //设置水平边距
            float horzMargin = pageWidth * (1 - scaleFactor) / 2;
            if (position < 0) {
                view.setTranslationX(horzMargin - vertMargin / 2);
            } else {
                view.setTranslationX(-horzMargin + vertMargin / 2);
            }
            // Scale the page down (between MIN_SCALE and 1)
            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);
            // Fade the page relative to its size.
            //根据图片目前尺寸进行颜色变化
            view.setAlpha(MIN_ALPHA + (scaleFactor - MIN_SCALE)
                    / (1 - MIN_SCALE) * (1 - MIN_ALPHA));
        } else { // (1,+Infinity]
            // This page is way off-screen to the right.
            view.setAlpha(0);
        }
    }
}
